Coupling efficiency between an optical fiber and a laser diode is limited by the accuracy and stability of the alignment achievable during the assembly process. Alignment of an optical fiber and a laser diode may be achieved by placing the optical fiber using a feature which has been etched onto a silicon ‘optical bench’, upon which the laser diode has already been precisely attached. However, this simple technique is limited in precision by the manufactured accuracy of the silicon and the fiber and subsequent movement due to thermal stresses during the joining process. Another technique uses a mount to support the optical fiber. Once the laser and the optical fiber have been aligned and attached to the bench, the mount is mechanically deformed until an optimum coupling efficiency is achieved. However, this technique suffers from the disadvantage of creep or flow of the deformed material and is therefore not stable in the long term. Creep is a natural result of the aging process, but is more acute where materials are subjected to stress. Furthermore, the problem of creep is increased due to the high temperature to which such coupling assemblies are likely to be subjected. Such creep reduces the coupling efficiency between the laser and the fiber as the assembly ages.
In the coupling device of this invention a high coupling efficiency between a fiber and a laser diode is aimed for, therefore it is important that the fiber tip is at an optimum distance from the laser diode, typically between 5 μm and 10 μm from the laser facet. However, as the fiber tip is so close to the output facet of the laser this means that a small displacement from the optimum position causes a significant drop in coupling efficiency. At distances further from the output facet of the laser, displacements from the optimum position do not have such a great effect but coupling efficiency is reduced. Therefore it is important in a coupling device which is aiming for a high efficiency of coupling that the device is stable, i.e. that ageing does not cause the tip of the fiber to be displaced even a small amount from an optimum coupling position.
This invention serves to alleviate such problems of reliability and stability, and is particularly beneficial for components requiring high reliability.